(1) Field of the Invention
The present invention generally relates to terminal equipment used in an optical communication system, and more particularly to an improvement in a data link process of transferring a variety of information between terminal equipments, between the terminal equipment and a repeater, or between the repeaters.
(2) Description of the Prior Art
FIG. 1 shows a system using a conventional data link system. The system shown in FIG. 1 includes two terminal equipments 1 and 3, and a regenerative repeater 2. The terminal equipment 1 and the repeater 2 are connected to each other via an optical transmission path, and the terminal equipment 3 and the repeater 2 are coupled to each other via an optical transmission path. The terminal equipments 1 and 3 are installed in stations A and C, respectively, and the repeater 2 is installed in a station B. The system thus configured is a so-called point-to-point type optical communication system. The terminal equipments 1 and 3 have controllers 5-1 and 5-3, respectively, and the repeater has a controller 5-2. The controllers 5-1 and 5-2 are connected to each other via a control line, and the controller 5-1 and 5-3 are connected to each other via a control line. Information is transferred between the terminal equipments 1 and 3 and the repeater 2 via the optical transmission paths. Control information used for monitoring operations of the terminal equipments 1 and 3 and the repeater 2 is transferred between the controllers 5-1 and 5-2 and between the controllers 5-1 and 5-3. For example, the controller 5-1 of the terminal equipment 1 collects control data about the repeater 2 and the terminal equipment 3 output by the respective controllers 5-2 and 5-3.
The data link system shown in FIG. 1 cannot be applied to a system based on a back-to-back structure as shown in FIG. 2. As shown in FIG. 2, a terminal equipment 4 having a controller 5-4 is installed in the station C, and a terminal equipment 5 connected to the terminal equipment 4 via an optical transmission path is installed in a station D. The terminal equipment 5 has a controller 5-5. It should be noted that electric signals carrying information are transferred between the terminal equipments 3 and 4. It may be considered that a new optical communication system composed of the terminal equipments 4 and 5 is added to the previously used optical communication system shown in FIG. 1. The above back-to-back system is used when the terminal equipment 3 does not have an afford for accommodating another optical transmission path.
The data link system of the system shown in FIG. 2 is configured as follows. Supervisory devices 6-1-6-5 are connected to the controllers 5-1-5-5, respectively. The supervisory devices 6-1-6-5 monitor the operations of the devices 1-5, respectively. Control information collected at the supervisory devices 6-1-6-5 is transmitted, via respective modems 7-1-7-5, to a modem 8 of a centralized supervisory station. It should be noted that lines connecting between the modems 7-1-7-5 and the modem 8 are provided separately from the optical transmission lines. The control data received via the modem 8 is sent to a master supervisory device 9, which executes a remote control operation on the devices 1-5 on the basis of the collected control data.
However, the system shown in FIG. 2 has a disadvantage in that the master supervisory device 9 is provided outside of the devices 1-5 and needs an additional area for installation.